Tent

ABSTRACT

An insulated tent which has interior and exterior walls that are separated from each other by an atmosphere of low thermal conductivity. The atmosphere may be a partial vacuum or may include a gas with lower thermal conductivity than air. The walls may be kept separate by the pressure of the gas or by mechanical forces and the partial vacuum may be induced by means of a one-way valve which permits the escape of heated air from between the interior and exterior walls. Also disclosed are structures that reduce the effect of wind on the tent&#39;s exterior surface, including spoilers and convex windward edges, and structures that guide the flow of water on the interior and exterior surfaces of the tent.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present patent application claims priority from U.S. provisional patent application 61/023,924, Hollinger, Improved tent, filed Jan. 28, 2008. That application is incorporated by reference into the present patent application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention has generally to do with tents, and more particularly a portable tent that protects its occupant from exposure to hazardous weather conditions including forces of extreme winds and frigid temperatures.

2. Description of Related Art

Tents are typically expected to protect their occupants from exposure to elemental forces of wind, rain, sunlight and the pelting of snow, sand and other windblown particulates. High-performance tents may be expected to provide their occupants with a measure of protection from extreme exposure to frigid polar climates, searing deserts and gusty mountaintops.

A tent must provide shelter while being collapsible, easily packed and transported. In order to be portable, a tent must overcome a unique set of challenges by comparison with an immobile structure. While thick layers of fiberglass insulation and a concrete foundation are suitable to protect occupants of a house from frigid temperatures and gale-force winds, for example, such materials would be entirely unsuitable for construction of a portable tent.

A tent is ordinarily expected to address a range of practical issues, among them:

-   1. Shelter. A tent provides shelter, with an interior volume     adequate in size for at least one human occupant. -   2. Protection. A tent protects its occupant from exposure to     elemental forces of wind, rain and snow. -   3. Durability. A tent must be constructed to resist wear and tear     during repeated stresses of unpacking and repacking. -   4. Health Safety. A tent must provide for the safe respiration of     occupants and evacuation of uncomfortable and potentially dangerous     condensation. -   5. Visibility and Access. A tent must provide its occupants with     adequate connections between interior and exterior environments. -   6. Portability. A tent is generally expected to be collapsible,     lightweight and easily transported by one person. -   7. Affordability. Because a tent is considered a consumer commodity     and in many regions of the world a tent is a necessity for survival,     material costs and manufacturing processes must be important     considerations. -   8. Environment. Because a tent is often erected in a natural     environment, it should impose minimal impacts on its footprint and     surroundings.

PRIOR ART

Two views of an example tent are shown in FIGS. 1A and 1B. The view at 100 shows sidewall 101 and upper wall 102. Flexible tent rods 103, by attachment to the tent walls at connection points 104, provide structural support to prevent the tent from collapsing and also to maintain the tent's shape while resisting forces of wind, rain and snow acting on exterior surfaces.

An exploded view of the same tent is shown at 110 with sidewall 111 pulled back to expose the tent interior. The tent has single-ply walls, each having an exterior surface facing the outside environment and an interior surface on its reverse side facing the occupiable area of the tent. The entire volume contained by the tent walls is usually available for occupancy by the tent user. Tent door 112 provides access and egress for tent users through a zippered opening seamed into a tent wall.

Tents of prior art describe lightweight materials and means for providing added protection and comfort to occupants. Among these are double-wall tents and insulated tents.

An example double-wall tent is shown at 200 in FIGS. 2A and 2B. An exterior wall is a layer of single-ply fabric 201, commonly referred to as a rainfly. The rainfly is stretched taut over the tent poles and fabric of single-wall tent 202. The rainfly is typically pulled taut at a few points along its perimeter, such as shown at tie-down 203, where it is tethered to either the tent base or to tent stakes driven into the ground.

In exploded view 210, outer sidewall 211 and inner sidewall 212 are pulled back to reveal the inside of a double-wall tent. Air gap 213 is the space between rainfly 214 and interior wall 215. Tent poles 216 pass through the air gap, supporting both walls of the tent and providing structural resistance to elemental forces. Tie-downs as shown at 217 keep the rainfly taut over the tent poles and the interior wall.

The rainfly is typically constructed of a hydrophobic material that directs rainwater away from the tent, preventing direct contact with the interior wall and thereby reducing the introduction of moisture into the tent interior. Protected from direct exposure to rainwater, the interior wall may have portions that are constructed of a mesh or breathable fabric that allows for escape of moisture within the tent generated by the occupant's respiration or perspiration.

The air gap of a double-wall tent serves a number of important functions. Air gap 213 is open to convection of fresh air entering beneath rainfly 214 at its exposed perimeter edge 218. This fresh air passing between inner and outer walls facilitates evaporation of condensation from within the tent.

By promoting circulation of fresh air, air gap 213 also provides for the health and safety of the tent occupant. Ventilation is critically important if the tent's exterior wall or rainfly is predominately constructed of an air-impermeable material that would otherwise create a suffocating condition within the tent interior.

The air gap between walls of a double-wall tent of prior art, even one of the type shown at 213 that is open to convection of fresh air, acts as a thermal barrier between the outer environment and the tent interior. Air molecules within the air gap are limited in movement, thus inhibiting the transfer of energy between exterior and interior environments.

Although a double-wall tent with an air gap may provide a measure of thermal protection, is not an optimal system for protecting the occupant from exposure. Air molecules at normal atmospheric pressure, though somewhat confined in motion within an air gap, remain subject to convective forces that promote the transfer of energy between the exterior and interior environment.

Multi-layer and multi-cell insulative materials described by tents of prior art offer significant reductions in thermal conductivity between exterior and interior tent surfaces. Materials such as Polar Guard, 3M Thinsulate and aerogels, while air-permeable, inhibit movement of air molecules and thereby reduce the transmission of thermal energy between the outdoor environment and tent interior. Other materials such as foam insulation, which are semi-permeable or impermeable to the passage of air, operate similarly to porous insulators by limiting movement of air molecules between exterior surfaces.

Although insulative materials offer thermal protection from extreme conditions, these same materials present a number of problems that must be considered in the manufacture of a tent. Specifically, problems with insulative materials are:

-   -   1. Poor durability. Insulative materials lose effectiveness with         the repeated compactions ordinarily associated with the normal         packing and unpacking of a camping tent.     -   2. Trapping of moisture. While insulative materials improve in         effectiveness as a function of thickness, an increase in the         thickness of a tent wall has an adverse impact on the escape of         moisture within the tent interior and in the accumulation of         moisture within the insulation layer.     -   3. Poor portability. While insulative materials improve in         effectiveness as a function of thickness, an increase in the         thickness of a tent wall has an adverse impact on weight,         storage volume and portability.     -   4. Cost factors. Raw material costs of insulative materials may         be cost-prohibitive.     -   5. Fabrication issues. Construction costs in the stitching and         seaming of thick, insulative materials may be cost-prohibitive,         especially when provisions for tent access and visibility are to         be seamed into tent walls.     -   6. Degradation. Polymer-based insulative materials may be         susceptible to degradation by continued exposure to ultraviolet         radiation from sunlight.     -   7. Environmental factors. Insulative materials may be composed         of chemical compounds that are unsuitable for use as         environmental and sustainability standards advance. Commonly         used plastics are neither biodegradable nor recyclable.     -   8. Health safety factors. Health impacts must be of particular         concern in the fabrication of a tent with insulative materials         because of the tent's potential to concentrate fumes and         particulates within its confined atmosphere. Insulative         materials may contain chemical compositions with health impacts         that must be mitigated to ensure the safety of camping tent         occupants. Ceramic aerogel and fiberglass insulations may         require special care to reduce direct contact or inhalation of         particulates captured in the confined atmosphere of a camping         tent. Plastics and other materials, even those that are treated         to be flame-retardant, may release hazardous fumes if         accidentally burned in an enclosed space. Chemical compounds         such as PVC and plasticizers are susceptible to off-gassing of         noxious vapors.

As an alternative to insulative materials, a heating system is capable of providing protection from frigid conditions. Electric and fuel-burning systems of prior art are capable of providing heat to tent occupants. Such systems, however, and the energy sources to drive them such as solar cells, wind turbines, batteries and fuels are cumbersome and poorly equipped to meet the demands of a lightweight, portable tent deployed in a variety of environments and climatic conditions.

Wind Resistance in Prior Art

Tents of prior art may be considered streamlined in that the typical curve-shapes of exterior surfaces promote laminar airflow. Because a tent must include an encapsulated area suitable in size for the occupancy of at least one person while maintaining a minimal footprint size on the tent site, the tent's exterior surface of curvature is, however, sufficiently bluff-shaped to make the tent susceptible to the impacts of high-pressure forces acting on its windward side and the formation of a low-pressure bubble on it's leeward side when exposed to high winds.

An typical aerodynamic interaction with a portable camping tent is shown in FIGS. 3A-3E. Tent 300 has rainfly 301 stretched over inner wall 302. Side view 310 and top view 320 of tent 300 show more clearly that the rainfly, here illustrated respectively at 311 and 321 in phantom lines, closely envelopes the shape of the inner wall 312 and 322.

Winds generally strike a tent from a direction lateral to the ground plane. Illustration 330 shows a typical interaction between wind and the example tent of 300. Light breeze 331 flows along the laminar surface of the rainfly, following the curve of the windward surface. As illustrated using arrows to depict airflow, the laminar layer of air moves up to the tent's crown-point and then dips at 332, following the downward curve of the leeward surface. In a light breeze, such a tent shape may be dominated by friction drag rather than pressure drag and thus be considered streamlined. Pressure impacts on the windward and leeward surfaces are minimal.

As shown at 340, the bluff shape of the tent becomes problematic in high-wind conditions. On the windward side of the tent, air striking the tent's steeply sloped windward surface is captured in a pocket between the ground plane and the swiftly moving airstream shown by arrows at 341. The airstream interacting with the windward tent surface forms high-pressure bubble shown by arrows at 342. High-pressure bubble 342 becomes a virtual surface over which high-speed air layer 341 passes. Unfortunately for the tent occupant, high-pressure bubble 342 exerts force on the tent wall as shown at windward surface 343.

Other problems exist on the leeward side of the bluff-shaped tent of 340. Separation of the laminar layer of high-speed air as shown along the arrow paths aft of the tent's crown point at 345, forms low-pressure pocket shown by arrow path 346 behind the tent. Here, arrow 346 shows the path of air being pulled toward the tent and then pulled outward by high-speed airstream 345. Low-pressure pocket 346 has an adverse impact on the tent, sucking the tent wall outward as shown at leeward surface 347.

Even in moderate conditions, forces of lift acting on tent surfaces can become problematic for lightweight tent fabrics and structures to resist.

To improve protection in moderate and high winds, the exterior surface of a double-wall tent can be extended to sweep over a wider footprint than the occupied portion encapsulated by the interior wall. As the tent's footprint is extended, the slope of the tent's exterior surface is reduced with respect to wind arriving parallel to the groundplane, promoting the laminar flow of air from its windward to leeward side.

For example, an example double-wall tent shown at 400 in FIGS. 4A-4E has a rainfly with a broadened scope by comparison with the tent of FIG. 3. A second view of this tent at 410 shows that the shape of the rainfly, here illustrated in phantom lines at 411, varies considerably from inner wall 412.

In high winds as shown at 420, the broadened rainfly allows the high-speed layer to pass along the gentle sweep of its contoured surface. The laminar airflow along a broadened rainfly may be more suitably disposed to lateral winds to prevent the formation of a high-pressure bubble on the windward side and a low-pressure bubble on the leeward side.

Unfortunately for the tent occupant, forces of lift acting on the broadened rainfly of 420 may still cause the leeward tent surfaces to rise, pulling upward on the tent structure and tent stakes which are generally constructed to resist downward force. Other adverse interactions may occur because the tent surfaces are in direct contact with the high-speed airstream. For this reason, it is advantageous to consider improvements to buffer the high-speed airstream from interaction with the tent's exterior surfaces.

Another adverse interaction between aerodynamic forces and a typical tent occurs when the wind strikes the edge of the rainfly. Wind striking such a sharp edge creates a turbulent condition that causes the edge and margin to flutter. This turbulent condition also may have a detrimental impact on the promotion of a laminar flow of air up and over the rainfly.

To illustrate an edge that is typically prone to failure, tent 430 has rainfly 431 pulled taut over inner wall 432. The shape of this rainfly is maintained by the tension exerted across its surface by tie-downs 433 along its perimeter edge. A portion of the rainfly edge at 434 is shown in an enlarged view at 440. Sharp edge 442 of rainfly 441 is an example of an edge that is prone to promoting an undesirable turbulent condition when it is disposed as a leading edge to wind.

Waterflow and Condensation in Prior Art

Tents of prior art describe a number of methods for management of waterflow and condensation.

The perspiration and respiration of moisture from a tent occupant may cause condensation to form on interior walls. In cold weather, the condensation can freeze on interior surfaces and may present an uncomfortable or dangerous condition. To reduce the negative effects of condensation and frost on the tent's inner surfaces, breathable fabrics facilitate the escape of water vapor from the tent interior. Wicking materials are used in insulating layers to draw moisture away from areas where condensation is unwanted. Condensation barriers capture and direct condensation forming on the tent's interior surfaces.

Raindrops falling on a tent surface may be pulled by gravitational forces downward, entering the tent through vents, windows or doors. To better manage waterflow, tents of prior art describe fabric gutters, seamed onto exterior surfaces, to capture water and direct water to suitable collection or exit locations.

Advanced hydrophobic materials used in the fabrication of tent rainflies are capable of repelling rainwater, causing droplets to flow off of and away from a tent's exterior surface.

Tents of prior art, designed for use in arid environments, direct rainwater to collection points for purification and eventual use as drinking water.

OTHER PRIOR ART

U.S. Pat. No. 5,411,047 describes a modular tent structure capable of withstanding high winds.

U.S. Pat. No. 4,705,717 describes a double-wall composite material that acts as an insulative barrier.

U.S. Pat. No. 4,102,352 describes a double-wall tent with modular insulated rooms.

U.S. Pat. No. 5,913,772 describes a hammock with condensation collection and runoff features.

U.S. Pat. No. 5,035,253 describes a rain awning for collecting runoff from a tent canopy.

U.S. Patent application 20070154698 describes aerogel textile-like blankets that can be used in the production of insulated tents.

The improved umbrella of published U.S. Patent application PCT/US/2006/000630 describes an aerodynamic leading edge at the edge of an umrella, gutters that act as guides on the upper surface of an umbrella canopy and turbulence-inducing spoilers on the upper surface of an umbrella canopy.

Inflatable tents and air mattresses of prior art describe the use of an airtight membrane to retain a high-pressure atmosphere within the tent, the tent floor or the tent walls. Because air in an enclosed high-pressure chamber has greater thermal conductivity than air in an enclosed chamber at normal atmospheric pressure, inflatable compartments are not optimal insulators.

BRIEF SUMMARY OF THE INVENTION

The object of the invention is achieved by a tent that has a portion of interior and exterior walls that are separated from each other by an atmosphere of lower thermal conductivity than air of the tent's operating environment. The atmosphere may be a partial vacuum or it may be an atmosphere dominated by an inert gas with lower thermal conductivity than air such as Argon. The insulative compartment may be sealed airtight or it may be constructed using semi-permeable materials and combined with active means for periodic evacuation of air and regulation of air pressure.

In other aspects of the invention, the formation of the low-pressure atmospheric condition is facilitated by the heating of air within an airtight compartment through the capture of solar radiation, the release of air pressure from the compartment through a relief valve, and the subsequent cooling of air within the compartment.

In other aspects of the invention, the formation of the low-pressure atmospheric condition is facilitated by the heating of air within an airtight compartment by active means, the release of air pressure from the compartment through a relief valve, and the subsequent cooling of air within the compartment.

In other aspects of the invention, the formation of the low-pressure atmospheric condition is facilitated by the forced separation of exterior and interior surfaces when the tent is erected.

In other aspects of the invention, the active promotion of a low-pressure atmospheric condition between the tent's exterior and interior walls facilitates the evacuation of condensation from the tent's interior, occupiable area.

In other aspects of the invention, the active promotion of a low-pressure atmospheric condition between the tent's exterior and interior walls facilitates the capture of rainwater and moisture from the tent's exterior and interior surfaces for the purpose of collecting a supply of potable water.

In other aspects of the invention, the low-density gas may be injected between exterior and interior surfaces of a sealed compartment.

In other aspects of the invention, the low-density gas within the insulative compartment is molecularly separated from the tent's operating environment.

In other aspects of the invention, an airtight sleeve with openings on opposing sides of the tent's exterior surface allow for the passage of tent rods without compromising the insulative integrity of the area between the tent's exterior and interior surfaces.

In other aspects of the invention, the sleeve passing through the tent is integrated into the exterior wall so that a tent pole passing through the sleeve to support the tent has minimal interactions with aerodynamic forces of wind acting on exterior surfaces.

In other aspects of the invention, the perimeter edge of the exterior tent surface that is a leading edge with respect to lateral winds is substantially convex, thereby dampening the turbulence-caused flapping or fluttering normally associated with wind striking a sharp edge.

In other aspects of the invention, portions of the tent's exterior surfaces are roughened to act as aerodynamic spoilers when the tent is buffeted by wind, creating a thin unseparated layer of turbulence between the tent's surface and the layer of laminar airflow and thereby reducing adverse friction-based interactions with the tent's exterior surfaces.

In other aspects of the invention, the roughened portions of the exterior membrane that act as aerodynamic spoilers are meshed screens which also allow for the controlled intake of fresh air, exhaust of respired air from the tent occupants, and evacuation of condensation.

In other aspects of the invention, the roughened portions of the exterior membrane that act as aerodynamic spoilers are a series of slightly raised wires running concentrically around the tent substantially parallel to the ground plane and integrated into the tent's exterior surface to also provide structural integrity to the exterior surface.

In other aspects of the invention, a lift spoiler on the exterior surface of the tent surface spoils laminar airflow in order to reduce forces of lift acting on the tent.

In other aspects of the invention, a deflector on the exterior surface of the tent surface deflects wind and thereby creates a virtual surface for the airstream to pass over, thereby reducing direct interactions between the moving airstream and other tent surfaces.

In other aspects of the invention, a ring of a substantially smooth surface bands the perimeter margin of the tent's exterior surface, separated from the occupiable area of the tent by a gap or a band of air-permeable material such as netting, mesh or screen and acting as a wind deflector to create a virtual surface of a single surface airfoil, directing airflow above the tent's occupiable area and thereby reducing interaction between high winds and the exterior surfaces covering the occupiable area of the tent.

In other aspects of the invention, one or more windsocks are seamed into the tent's exterior surface to allow for the escape of air pressure captured beneath the exterior surface, and otherwise collapsing onto the exterior surface in order to prevent the entry of rainwater into the tent.

In other aspects of the invention, a series of textured ridges or perturbations are fabricated into the tent's exterior and interior surfaces to promote the directional flow of rainwater and condensation towards a desired location without capturing the water within a confined channel or gutter.

In another aspect of the invention a gutter that captures and directs waterflow causes the rainwater to move in a spiral around the tent to a single collection point at the tent perimeter edge.

In other aspects of the invention, the perturbations and gutters that guide waterflow also function as aerodynamic spoilers to roughen airflow in the formation of an unseparated turbulent layer.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIGS. 1A and 1B show an ordinary single-wall portable tent;

FIGS. 2A and 2B show an ordinary double-wall tent;

FIGS. 3A-3 E illustrate the effects of winds on a bluff-shaped tent;

FIGS. 4A-4E illustrate the effects of winds on a broadened rainfly and at the edge of a rainfly;

FIGS. 5A and 5B illustrate tents with insulating walls;

FIGS. 6A and 6B show how a low-pressure atmosphere may be introduced into an insulating wall by separating its surfaces;

FIGS. 7A-7E show how a low-pressure atmosphere may be introduced into an insulating wall through a one-way valve;

FIGS. 8A-8C illustrate the effects of wind and low-pressure forces acting on an insulating wall;

FIGS. 9A and 9B illustrate structures that prevent the collapse of an insulating wall and that prevent the catastrophic loss of atmosphere within an insulating wall;

FIGS. 10A-10F illustrate a sleeve that allows for the isolated passage of a tent rod through the tent;

FIGS. 11A-11C illustrate windows for and methods of access and egress to a tent with an insulating wall;

FIGS. 12A-12C illustrate gutters of the guide type;

FIGS. 13A-13C illustrate gutters of the spiraling channel type;

FIGS. 14A-14C illustrate a rainfly with an aerodynamic leading edge and the effects of wind striking such an edge;

FIGS. 15A-15C illustrate spoilers that promote a thin layer of turbulence and the effect of wind acting on such spoilers;

FIGS. 16A-16I illustrate a deflector that directs air over a virtual surface above the tent;

FIGS. 17A-17D show how windsocks may be used to relieve air pressure under the rainfly; and

FIGS. 18A-18D illustrate a combination tent that combines various ones of the innovations disclosed herein.

DETAILED DESCRIPTION OF THE INVENTION

As an object interacting with extreme temperature conditions and forces of wind, rain and windblow particulates, a conventional tent may be improved according to its insulating and aerodynamic properties. An understanding of low-speed airflow around moving bodies has helped produce optimal designs for bike helmets, flying discs, model airplanes and umbrellas.

The Insulating Wall

The primary embodiment of the tent of this invention is constructed of walls that are comprised of at least three component layers: an outer surface hereinafter called the Exterior Membrane; an inner surface hereinafter called the Interior Membrane; and a layer between the Exterior Membrane and Interior Membrane hereinafter called the Internal Gap.

The combination of an Exterior Membrane, Interior Membrane and Internal Gap, along with specific atmospheric conditions within the Internal Gap further described herein, together form an Insulating Wall. The primary function of the Insulating Wall is to provide a barrier between extreme environmental conditions and the inhabitable area of the tent.

The Internal Gap contains either a low-pressure atmosphere or a high-density, inert gas such as Argon.

As seen from its exterior, a tent with an Insulating Wall may appear identical to a tent of prior art as shown at 100 in FIGS. 1A and 1B.

Exploded views of a tent with an Insulating Wall are shown in FIGS. 5A and 5B. As shown at 500, Exterior Membrane sidewall 501 is pulled away to reveal Interior Membrane 502 inside Exterior Membrane 503. In this example the Interior Membrane has a similar shape to the Exterior Membrane and is encapsulated within the Exterior Membrane. Internal Gap 508 exists between the Exterior Membrane and Interior Membrane. In this example, tent poles 504, illustrated in phantom lines because they are not required component parts of an Insulating Wall, pass outside of the tent and support the Exterior Membrane at connection points 505.

A second exploded view of a tent with an Insulating Wall is shown at 510. Here, Exterior Membrane sidewall 511 and Interior Membrane sidewall 512 are pulled away to reveal inhabitable area of the tent at 513 inside Interior Membrane 514.

The portion of tent floor at 515 within the occupiable area of the tent does not conform to the definition of an Insulating Wall because its interior and exterior surfaces are substantially coplanar, offering no separation between its interior and exterior surfaces and therefore no Internal Gap. In this example tent, Exterior Membrane 519 and Interior Membrane 514 are seamed together at the perimeter edge 518 of floor 515.

The portion of tent floor at 520 that is outside the occupiable area of the tent is part of the External Membrane. Its inner surface faces into the Internal Gap and its outer surface faces the ground beneath the tent. The ground beneath the tent is considered part of the outdoor environment, and an Insulating Wall may be useful in protecting the tent occupant from exposure to snow, ice or other ground conditions.

It is quite possible for an entire tent floor to be constructed as an Insulating Wall by having an Exterior Membrane on the ground plane, an Interior Membrane raised above the ground plane and an Internal Gap containing a thermally insulative atmosphere between the two membranes. The Insulating Wall of a tent floor may be a continuation of an Insulating Wall running along the side of a tent, or it may be an independently functioning Insulating Wall.

Because the Internal Gap is expected to contain either a low-pressure atmosphere or a high-density gas such as Argon, the seams between tent surfaces are expected to be impermeable to the escape of the contained atmosphere. These airtight or gas-impermeable seams include those at the perimeter edges of sidewalls 511 and 512.

Although it is anticipated that atmospheric pressure within the Internal Gap will vary from that of the external environment, atmospheric pressure within the occupiable area of the tent of this invention is assumed to be generally at equilibrium with the external environment. An opening such as air vent 516 would allow air to pass between the tent's external environment and its occupiable interior space without impacting the atmosphere within Internal Gap 517. More effective means for providing ventilation to the occupiable area of the tent are described in Section B-5.

Tent doors and windows have been omitted from FIGS. 5A and 5B and many other figures described herein. Although tent doors and windows are an essential part of a portable tent, they are not essential to the functionality of an Insulating Wall. Tent doors and windows can co-exist with an Insulating Wall as demonstrated in Section B-5.

The Exterior Membrane sidewall as shown at 511 in FIGS. 5A and 5B is an integral part of the Exterior Membranes of each example tent illustrated in FIGS. 6A and 6B, FIGS. 7A-7E, FIGS. 8A-8C, FIGS. 9A and 9B, FIGS. 11A-11C and example tents illustrated at 1000, 1010, 1020 and 1030 in FIGS. 10A-10F, but is omitted from those side views to allow variations of interior parts within the Exterior Membranes of those tents to be made visible.

The Interior Membrane sidewall as shown at 512 in FIGS. 5A and 5B is an integral part of the Interior Membranes of each example tent illustrated in FIGS. 6A and 6B, FIGS. 8A-8C, FIGS. 9A and 9B, FIGS. 11A-11C, example tents illustrated at 700 and 740 in FIGS. 7A-7E and example tents illustrated at 1000, 1010, 1020 and 1030 in FIGS. 10A-10F, but is omitted from those side views to allow variations of interior parts within the Interior Membranes of those tents to be made visible.

The sidewall as shown at 111 in FIGS. 1A and 1B is an integral part of the single-wall tent of illustrations 1040 and 1050 in FIGS. 10A-10F, but is omitted from those side views to allow interior parts to be made visible.

The Insulating Wall is further described in the following sections.

A. Internal Gap Atmosphere

-   -   1. The sealed low-pressure vacuum     -   2. The onsite low-pressure vacuum     -   3. The active low-pressure vacuum     -   4. The sealed low-density gas     -   5. The injected low-density gas     -   6. The collected low-density gas     -   7. Regulators

B. Insulating Wall Structures

-   -   1. Structure of Exterior Membrane     -   2. Structure of Interior Membrane     -   3. Structure of Internal Gap     -   4. Insulating Sleeve     -   5. Access, Egress, Windows and Vents     -   6. Breathable Fabrics

Other improvements to the tent of this invention that may be beneficial to a tent with or without an Insulating Wall are further described in the following sections:

C. Hydrodynamic and Aerodynamic Improvements

-   -   1. Microgutter     -   2. Spiral Gutter     -   3. Other waterflow-related improvements     -   4. Aerodynamic Leading Edge     -   5. Turbulence-Inducing Microspoiler     -   6. Lift Spoilers     -   7. Airstream deflector     -   8. Windsocks

D. Combinations

A. Internal Gap Atmosphere

The atmosphere within the Internal Gap is either low-pressure air or it is a composition dominated by an inert gas of a higher density than air such as Argon.

The “normal atmospheric pressure” often referred to in this document is the atmospheric pressure of the outdoor environment in which the tent is deployed for occupancy.

The “low-pressure atmosphere” often referred to in this document is defined by a pressure that is lower than normal atmospheric pressure. When contained within an Internal Gap for the purpose of insulation, the low-pressure atmosphere is sufficiently lower than normal atmospheric pressure so as to be characterized by a measureable decrease in thermal conductivity between Exterior and Interior Membranes.

When contained within an Internal Gap for the purpose of capture and collection of moisture, the low-pressure atmosphere is sufficiently lower than normal atmospheric pressure so as to be characterized by the measureable forces of a vacuum acting on its moisture-collecting surfaces.

Although it is anticipated that the elemental composition of the “low-pressure atmosphere” will be substantially that of ordinary air, it is possible that other gases may be backfilled at low-pressure to offer the same or better insulative benefit as low-pressure air.

Sections A-1, A-2 and A-3 further describe an Insulating Wall containing a low-pressure atmosphere.

A container of Argon or similarly dense gas has lower thermal conductivity than an identically-sized container of air at the same atmospheric pressure. To create an effective insulator, the atmosphere within the Internal Gap may be dominated by Argon or any other similarly inert, high-density gas. If a high-density gas such as Argon is used to fill the Internal Gap, atmospheric pressure within the Internal Gap may be at lower, higher or the same atmospheric pressure as normal atmospheric pressure.

Sections A-4, A-5 and A-6 describe an Insulating Wall with a high-density gas-filled atmosphere.

A-1. The Sealed Low-Pressure Vacuum

In one embodiment of the tent of this invention, the Insulating Wall contains a low-pressure atmosphere sealed into the Internal Gap during manufacture to eliminate further need for maintenance, repeated evacuation of air or regulation of air pressure by the tent user. In this sealed system, perimeter edges of Exterior and Interior Membranes are seamed together to retain a vacuum within the Internal Gap.

In this embodiment, Exterior and Interior Membranes are constructed using lightweight materials that are impermeable to the passage of air molecules, such as Mylar.

The Internal Gap with a sealed vacuum may be structured as a single low-pressure compartment, or it may be structured as a multi-cell low-pressure compartment. Structural alternatives are considered in Section B of this document.

The Internal Gap may be filled with independent substructures that provide the same net atmospheric condition and insulative benefit as an Internal Gap with a single low-pressure compartment or multiple low-pressure cells. For example, insulating capsules such as low-density ceramic microspheres may be sandwiched between the Exterior and Interior Membranes during manufacture. Ceramic microspheres are micron-sized lightweight hollow capsules with a ceramic outer shell and a low-pressure, low-density atmosphere captured within the shell. A collection of sandwiched microspheres can collectively provide an effective barrier to thermal transfer between the Exterior and Interior Membranes.

If the Internal Gap is packed with low-pressure capsules such as ceramic microspheres, air pressure within the Internal Gap surrounding the capsules can be at equilibrium with that of the tent's operating environment. A benefit of this design is that the Exterior and Interior Membranes can be manufactured using air-permeable, breathable materials typically used for construction of camping tents. Another benefit of this design is that it eliminates the need for structural components otherwise required to resist implosive forces acting on the Exterior and Interior Membranes.

A-2. The Onsite Low-Pressure Vacuum

In another embodiment of the tent of this invention, the Insulating Wall is a permanently sealed compartment in which a low-pressure atmosphere is introduced into the Internal Gap by the forced separation of the Exterior and Interior Membranes when the tent is erected.

As the Exterior and Interior Membranes are drawn into tension with one another, the expanded airtight pocket within the Internal Gap has fewer air molecules per unit volume and thus achieves a low-pressure state.

As an example, tent 600 in FIGS. 6A and 6B is not yet fully erected. When tent rods 601 are detached from the Exterior Membrane the low-pressure Internal Gap collapses and the surface of the Interior Membrane approaches the surface of the Exterior Membrane. Forces of air pressure indicated by arrows at 602 squeeze the Interior and Exterior Membranes together until the atmospheric pressure within the Internal Gap approaches normal atmospheric pressure.

When the tent is erected as shown at 610, tent rods pull Exterior Membrane 613 outward as shown by arrows at 611 while Interior Membrane 614 is restricted from outward expansion by its shape, which pulls inwardly as shown by arrows at 612. The forced separation of the Exterior Membrane and Interior Membrane increases the volume of Internal Gap 615, thus lowering the atmospheric pressure within Internal Gap.

A-3. The Active Low-Pressure Vacuum

In another embodiment of the tent of this invention, air is actively evacuated from the Insulating Wall to create a low-pressure atmosphere.

Mechanical means such as vacuum pump may be attached to the Insulating Wall to remove air from the Internal Gap. A power source that uses solar, geothermal, wind, heat exchange, human power, steam, electrochemical or other readily available energy may be used to generate power to remove air from the Internal Gap.

An example mechanical system is shown at 700 in FIGS. 7A-7E. This tent uses solar-powered vacuum pump 701 to evacuate air from Internal Gap 702. In operation, the pump's suction tube 705 is applied to one-way air valve 703. Upon the application of low-pressure, air valve 703 opens and allows air to be evacuated from the Internal Gap. The removed air is expelled at exhaust 706. Air valve 703 prevents air from re-entering the Internal Gap when the vacuum pump is removed or disabled.

It is possible to evacuate air from the Internal Gap using the sun's energy and a pressure relief valve, without the need for a mechanical pump. Air contained within the Internal Gap is warmed by sunlight. Heated air within the Internal Gap is allowed to escape from the Internal Gap through a pressure relief valve. In the evening, when the air cools, the pressure relief valve prevents entry of air into the Internal Gap. The resulting condition is an Insulating Wall with a low-pressure atmosphere contained in the Internal Gap.

Such a system is shown at 710 in FIGS. 7A-7E.

Exterior Membrane 712 is substantially transparent to allow for unimpeded passage of radiant sunlight. Interior Membrane 713, shown here with hatching to indicate that it is a dark color, absorbs sunlight for conversion to heat energy.

Pressure relief valve 711 allows air within the Internal Gap to escape when pressure within the Internal Gap exceeds normal atmospheric pressure. Pressure relief valve 711 prevents air from entering the Internal Gap at any time, particularly when pressure within the Internal Gap is lower than normal atmospheric pressure.

Heat energy arriving on the Interior Membrane raises the temperature of air within the Internal Gap. Pressure relief valve 711 allows hot air to escape so that pressure within the Internal Gap remains at equilibrium with normal atmospheric pressure. When sunlight wanes in the evening, air within the Internal Gap cools, and the Internal Gap's pressure drops. Pressure relief valve 711 prevents the inflow of air, and the low-pressure Insulating Wall becomes an effective barrier to thermal transfer.

A closeup view of pressure relief valve 711 is shown at 720 and 730 in FIGS. 7A-7E. As shown at 720, the relief valve is in open position, reflecting its state when air pressure in the Internal Gap exceeds normal atmospheric pressure. Air enters the valve at 723, pushing plunger 722 upward and escaping at 721. As shown at 730, the relief valve is in closed position, reflecting its state when air pressure within the Internal Gap is lower than normal atmospheric pressure. Plunger 732 blocks passage of higher-pressure air at 731 into the low-pressure Internal Gap at 733. This type of relief valve allows air to be removed from the Internal Gap but does not allow air to enter the Internal Gap.

Evacuation of air from the Internal Gap through a pressure relief valve may be achieved by the occasional, limited application of heat. As shown in example tent 740, propane torch 741 has attachment 742 sealed into the Interior Wall that allows the tent occupant to heat air within Internal Gap 744. Once heated, the pressurized air within the Internal Gap may escape through pressure-relief valve 743 on the Insulating Wall. When the heat source is removed, air within the Internal Gap cools and pressure within the Internal Gap drops. The relief valve restricts airflow back into the Internal Gap, thus capturing a sealed, low-pressure atmosphere within the Internal Gap as an effective thermal barrier for the duration of the tent's occupancy.

Evacuation of air from the Internal Gap may be achieved by airtight attachment to a portable canister from which air had been evacuated in advance. This canister is attached to the Internal Gap and a one-way air valve is opened. As the vacuum within the canister pulls air from the Internal Gap, equilibrium is met at a pressure that is lower than normal atmospheric pressure. Such a canister-based application would be useful in an emergency, when the one-time use of the vacuum canister eliminated the need for transport and operation of other means for creating a vacuum. A highly portable vacuum canister may be used and subsequently refreshed by attachment to a less-portable mechanical pump powered by a car battery.

The one-way valves and pressure-relief valves that are used for evacuation of air from the Internal Gap of a tent may be integrated into the Interior Membrane. On tent 700, for example, if one-way valve 703 is integrated into the Interior Membrane instead of the Exterior Membrane, vacuum pump 701 could be placed and operated from inside the occupiable area of the tent instead of outside the tent as shown.

With the active evacuation of air from the Internal Gap, it becomes possible for the Exterior and Interior Membranes to be semi-permeable to the passage of air molecules, while maintaining a low-pressure atmosphere within the Internal Gap. Further consideration of breathable fabrics and other air-permeable configurations are described in Section B-6.

A-4. The Scaled Low-Density Gas

In another embodiment of the tent of this invention, the Internal Gap contains an atmosphere dominated by Argon or similarly dense gas by comparison with the molecular composition of air. Argon, lower in thermal conductivity than air at the same atmospheric pressure, is commonly used to create an insulative atmosphere within skin-diving dry-suits and double-pane windows.

Because an Argon-dominated atmosphere is an effective insulator at the same atmospheric pressure as the surrounding environment, an Argon-filled Insulating Wall may not require the addition of structural walls or supports to counter the implosive forces associated with a low-pressure air-filled Internal Gap.

An insulative gas such as Argon may be contained within individual cells inside the Internal Gap.

An insulative gas may be contained in individual capsules, such as Argon-filled ceramic microspheres, within the Internal Gap.

A-5. The Injected Low-Density Gas

An insulative gas may be injected through a valve on the Insulating Wall at the time the tent is erected, and released when the tent is packed.

A-6. The Collected Low-Density Gas

By attachment to the Insulating Wall to existing air separation systems, an insulative gas such as Argon may be captured onsite from available air and introduced into the Internal Gap. Separation technologies, for example molecular sieves, have advanced to a point where they are lightweight, affordable and could produce a limited volume of gas required for sufficient operation of the Insulating Wall.

A-7. Regulators

A pressure sensor may be used to monitor and respond to air pressure changes within the Internal Gap. If the pressure within the Internal Gap varies from a desired pressure, the sensor may signal an alarm or may trigger the evacuation of air from the Internal Gap.

An ordinary pressure sensor may be used to routinely activate a mechanical vacuum in the event of significant fluctuation in air pressure within the Internal Gap.

A highly sensitive pressure sensor may be used in combination with a low-capacity air pump to regulate minor fluctuations in air pressure within the Internal Gap. The advantage of a low-capacity pump is that it can be extremely small and lightweight.

Because the Internal Gap is anticipated to be a relatively low-capacity envelope, a low-capacity pump operating at high frequency can be as effective in regulating pressure within the Internal Gap as a high-capacity pump operating infrequently.

A pressure sensor may use a variety of means to sense a change in atmospheric pressure within the Internal Gap. For example, a pressure sensor may respond to a change in tension on the Interior or Exterior Membrane.

B. Insulating Wall Structures

If the Internal Gap contains a low-pressure atmosphere with respect to the tent's external atmospheric pressure, the Exterior and Interior Membranes must be capable of responding to implosive forces acting upon them.

Forces of air pressure acting on a tent with a low-pressure Internal Gap are shown at 800 in FIGS. 8A-8C. Here, Internal Gap 805 has lower pressure than the atmosphere outside the tent and within the occupiable portion of the tent. Arrows at 802 indicate the vectors of force acting inwardly on the surfaces of Exterior Membrane 803. Arrows at 801 indicate the vectors of force acting outwardly on Interior Membrane 804.

The forces required to separate the Exterior and Interior Membranes may be provided by the tension of tent poles, ribs or other structural members existing outside of the Internal Gap.

Alternatively, forces required to separate the Exterior and Interior Membranes may be provided by tent poles, ribs or other structural members that pass directly through the Internal Gap and push apart on Exterior and Interior Membranes.

B-1. Structure of Exterior Membrane

The Exterior Membrane must resist force of the low-pressure Internal Gap as it pulls the Exterior Membrane inward and towards the Interior Membrane.

The inward and downward vectors of force acting on the Exterior Membrane of tent 800 are similar to the vectors of forces of wind and rain that would act on any tent's exterior surface. For this reason, the Exterior Membrane may benefit by adopting the exterior shapes and structural members of a streamlined tent of prior art.

To illustrate, tent 810 is shown interacting with forces of wind indicated by arrows at 811. Tent poles 813 attached to Exterior Membrane 812 at connection points 814 resist forces of wind. These same tent poles and connection points are capable of acting to prevent the Exterior Membrane from the inward pressure of a low-pressure Internal Gap.

As shown in the examples of 800 and 810, the exterior shapes of tents streamlined to promote laminar airflow over exterior surfaces are particularly well-suited for the shape of the Exterior Membrane of the tent of this invention because the curved exterior surfaces and matching structural supports designed to resist external pressure from wind and rain are capable of resisting the inwardly implosive forces acting on an Exterior Membrane.

B-2. Structure of Interior Membrane

The Interior Membrane must have the structural framework or composition to resist gravitational forces pulling it downward, as well as forces acting on it that pull it toward the Exterior Membrane as air pressure within the Internal Gap is lower than outside the Internal Gap.

As shown by the example tent at 820 in FIGS. 8A-8C, the arched shape of Interior Membrane 822 may, by attachment to the tent floor, be self-supporting and without need for additional structural support. The low-pressure vacuum within Internal Gap 824 may be sufficient to keep the Interior Membrane raised above the occupiable area of the tent.

Forces of expansion shown by arrows at 82 push outwardly on Interior Membrane 822 as atmospheric pressure remains higher within the occupiable area of the tent than within Internal Gap 824. If Interior Membrane seams running at the perimeter edge of floor 823 are secured to the ground plane, forces of outward expansion acting on the Interior Membrane may be sufficient to keep the Interior Membrane from collapsing into the occupiable area of the tent.

To keep the Interior Membrane from falling into the tent interior in the event of a loss of pressure within the Internal Gap, a series of thin fabric attachments, strings or other connections can be made between the Internal Gap and the Exterior Gap to limit the maximum distance of separation.

Although the Interior Membrane may be constructed to generally match the exact shape of the Exterior Membrane, it is anticipated that the Interior Membrane may vary in shape from the Exterior Membrane to better resist the forces acting on it.

The Interior Membrane may require the addition of framing components, fabric sections or restraints to restrict its outward expansion toward the Exterior Membrane.

The Interior Membrane may be attached to the Exterior Membrane with a zipper or other similar fastener along its border. By zippered attachment, the Interior Membrane may be easily removed when the Insulating Wall is not required.

B-3. Structure of Internal Gap

The Internal Gap is the area between the Exterior and Interior Membranes. Because the Internal Gap must contain an atmosphere of a pressure or composition that varies from the tent's operating environment, it is anticipated that the Internal Gap may be sealed airtight or it may be semi-permeable to the passage of air and water molecules.

The Internal Gap may be constructed as a single-cell compartment between Exterior and Interior Membranes. Examples of a single-cell compartment Internal Gaps are shown in tents of FIGS. 5A and 5B, FIGS. 6A and 6B, FIGS. 7A-7E and FIGS. 8A-8C.

Subwalls within the Internal Gap may provide structural resistance to the implosive forces acting on it. For example, the Internal Gap of tent 900 in FIGS. 9A and 9B contains a series of hollow tubes shown at 901. These hollow tubes are open at their ends and share the low-pressure atmosphere within the Internal Gap. Because the tubes are each capable of resisting some compressive force, they may collectively provide the structural integrity necessary to resist implosive forces acting on the Exterior and Interior Membranes.

As another method to prevent the implosive collapse of the Internal Gap, Styrofoam beads may be sandwiched between the Exterior and Interior Membranes during manufacture. Once filled with these beads, air can be subsequently evacuated from the Internal Gap, either during manufacture or when the tent is in use. The vacuum-packed Styrofoam beads provide structural support necessary to resist the implosive forces acting on the Exterior and Interior Membranes while providing the necessary thermal insulation.

Protuberances on the inner surface of the Exterior and Interior Membranes such as dimples or ridges may prevent the collapse of the Internal Gap when a vacuum is applied. To reduce thermal transfer between the Exterior and Interior Membranes through these tiny protuberances, the protuberances may be designed to minimize contact with the inner surfaces within the Internal Gap and may be constructed using insulative materials.

Because a tear in a single-compartment Insulating Wall would result in the complete loss of insulating capability, multi-cell solutions are preferable. The Insulating Wall may be constructed of multiple isolated cells or bladders, each maintaining an independent low-pressure vacuum. The advantage of this design is that the tent is capable of maintaining its insulating capability even when a portion of the Exterior or Interior Membrane is torn.

An example tent with multi-cell Insulating Walls is shown at 910 in FIGS. 9A and 9B. This tent has a series of sealed, airtight tubes at 911 running within the Internal Gap. The low-pressure atmospheric composition and pressure within each of these tubes is isolated within the confines of each tube, thus limiting the catastrophic loss of the insulative capacity of an Insulating Wall in the event of a tear of the Exterior Membrane, the Interior Membrane or the failure of a single tube.

The air gaps between the tubes at 911 are contained within the Internal Gap and together share a single atmosphere that may be at low-pressure or normal atmospheric pressure. This shared atmosphere has a useful purpose. To achieve the advantages of the Active Low-Pressure Vacuum improvements of Section A-3, a multi-cell Insulating Wall may be constructed with a single one-way valve available to the tent user to apply a vacuum into the shared atmosphere. Each tube at 911 can have its own one-way valve that is completely contained within the Internal Gap, with one end of the valve facing the inside of the tube and the other end facing the shared atmosphere within the Internal Gap. As the tent user evacuates air from the single, external one-way valve, the pressure in the shared atmosphere drops and causes the one-way valves in each tube to open, creating a low-pressure condition in each tube. Thus, a tent user can apply a vacuum to a single valve, evacuate air from an array of cells, remove the vacuum, and retain the insulative advantages of a multi-cell structure with isolated low-pressure compartments.

B-4. Insulating Sleeve

One or more sleeves may seamed into the Exterior Membrane, each with openings at two opposing exterior sides of the tent. A sleeve provides for the isolated passage of a tent pole through the Internal Gap while maintaining the functional integrity of the Internal Gap as a barrier to thermal energy transfer between the external environment and the tent's occupied interior. To protect the integrity of a low-pressure atmosphere within the Insulating Wall, seams between the sleeve and the Exterior Membrane may be airtight, as may be seams between the sleeve and the Interior Membrane.

Examples of insulating sleeves are shown in FIGS. 10A-10E. Tent 11000 has insulating sleeve 1001, a hollow tube that allows air outside the tent to pass through openings at either side of Exterior Membrane 1002. Airtight seams at 1003 and 1004 protect the Internal Gap and occupiable area of the tent from exposure to outside air temperature, pressure and elemental composition.

As shown at 1010, tent pole 1011 can pass through sleeve 1012 without puncturing the surfaces of the Exterior Membrane or Interior Membrane. The tent pole remains exposed only to the tent's external environment. As shown at 1020, as tent pole 1021 is erected, the sleeve shape matches that of the bent pole, providing structural support to Interior Membrane 1022.

As shown at 1030, it is possible for a sleeve to pass through the Internal Gap without passing through the Interior Membrane into the occupiable area of the tent. Here, sleeve 1031 prevents Interior Membrane 1032 from outwardly expanding, thus protecting Internal Gap 1033 from implosion while allowing tent pole 1034 to provide structural integrity to the Interior Membrane.

As shown at 1040 and 1050, an insulating sleeve may be an advantageous addition to a single-wall tent. The sleeve allows for one or more tent poles to pass inside the tent without exposing the occupant to rain and frigid conditions. As shown at 1050, the sleeve removes the poles from interaction with wind, streamlining the tent by promoting the laminar flow of wind over its exterior surfaces.

Because the interior portion of the sleeve through which the pole passes is exposed to the external environment, the sleeve itself may be insulated.

B-5. Access, Egress, Windows and Vents

A tent with an Insulating Wall may have operable doors and vents, to allow for access, egress and the passage of air between the tent's occupiable interior and external environment. Doors, vents and windows are possible without compromising the isolated atmosphere contained within an Insulating Wall.

Because a tent with an Insulating Wall allows for areas of the tent to have single-ply walls it is possible for the same tent to have standard doors, vents and windows.

Given the unique topology of an Insulating Wall, a number of improvements to access and egress are anticipated. For example, a tent foyer may be constructed as a tube-like passage connecting the Exterior and Interior Membranes. While the foyer's interior surface was itself an Interior Membrane isolated from the Exterior Membrane, the tent's door at the end of the foyer could be further isolated from the tent's main area of occupancy.

An air vent that promotes convection of air from the exterior environment to the tent interior may be isolated from the Insulating Wall by seaming together the Exterior Membrane and Interior Membrane along the bounds of the vent.

A tent with an Insulating Wall may have single-pane windows, which are isolated from the Insulating Wall by seaming together the Exterior Membrane and Interior Membrane at the bounds of the windowpane.

A tent with an Insulating Wall may have double-pane windows, with one pane seamed into the Exterior Membrane and a matching pane seamed into the Interior Membrane.

Example windows for a tent with an Insulating Wall are shown at 1100 in FIGS. 11A-11C. This tent has a double-pane window with pane 1101 seamed into Interior Membrane 1107 and pane 1102 seamed into Exterior Membrane 1106. The Interior and Exterior Membranes of the tent are seamed together at 1105, with interior and exterior surfaces becoming coplanar to form wall 1103 with single-pane window 1104. Wall 1103 is separate from the tent's Insulating Wall.

Example doors for a tent with an Insulating Wall are shown at 1110 in FIGS. 11A-11C. Interior doorway 1111 provides tunnel passage 1112 through Internal Gap 1113, allowing for access and egress from the tent interior to the external environment without compromising the atmospheric pressure and elemental composition of the Internal Gap. The tunnel is attached at airtight seams to the Exterior Membrane at 1115 and to the Interior Membrane at 1114. A second door is provided on the other side of the tent. Interior Membrane 1116 and Exterior Membrane 1117 are seamed together at 1120, with interior and exterior surfaces becoming coplanar to form wall 1118 with access and egress provided through a single door at 1119. Wall 1118 is separate from the tent's Insulating Wall.

Tunnel 1111 demonstrates that an opening between the tent's external environment and occupiable space is possible without compromising an airtight Internal Gap. Such a tunnel may be used for providing ventilation and for maintaining normal atmospheric pressure within the occupiable area of the tent.

The seaming of Interior and Exterior Membranes at various areas of the tent would allow for integration of many specialized features. For example, areas of the tent may be designed with a single wall construction for the wicking of moisture or improved ventilation while other areas of the tent have an Insulating Wall designed to inhibit thermal transfer. An example vent for a tent with an Insulating Wall is shown at 1120 in FIGS. 11A-11C. Interior Membrane 1121 and Exterior Membrane 1122 are seamed together at 1123, with interior and exterior materials becoming coplanar to form wall 1124 with vent 1125. Wall 1124 is separate from the tent's Insulating Wall.

In this regard, it is anticipated that an Insulating Wall may operate in conjunction with important functions of other tent surfaces, including condensation barriers, rainflies, mattresses, sleeping bags, blankets and pockets.

B-6. Breathable Fabrics

The addition of an Insulating Wall to a tent may result in the excessive capture of moisture from the exhalation of tent occupants. Moisture removal systems of prior art such as condensation barriers and portable dehumidifiers may be sufficient in combination with the Insulating Wall to provide comfort to the tent occupants.

The Insulating Wall may be constructed as a portion of a tent's walls, with other walls acting to reduce the uncomfortable and possibly dangerous impacts of freezing condensation within the tent interior. As described in Section B-5, a portion of the tent that is separated from the Insulating Wall may be constructed using breathable fabrics.

The addition of vents passing through the Insulating Wall may allow the tent occupants to regulate circulation of air and evacuation of moisture. The application of breathable areas and vents with the amount of tent used for an Insulating Wall may be balanced according to a particular application.

Because the Internal Gap may be designed with active means for air evacuation such as a vacuum pump, the Interior Membrane can be semi-permeable in order to facilitate the movement of humid air from the tent interior through the Interior Membrane into the Internal Gap and out through the pump exhaust.

With the Interior Membrane's construction as a breathable surface, the Interior Membrane itself can serve as an intake for air moving from inside the tent into the Internal Gap. As long as the air pump's capacity exceeds the volume of air passing through the breathable Interior Membrane, the Internal Gap will maintain the necessary low pressure needed to operate as an effective barrier to thermal transfer between the tent's exterior to interior.

In arid environments, water capture may be an important function of an Insulating Wall. In this embodiment of the tent of this invention, the Exterior Membrane is fabricated using a material that allows for the passage of water molecules. With the active evacuation of air from the Internal Gap, the resulting low-pressure system facilitates the movement of moisture from the tent's exterior surfaces, through the Exterior Membrane and into the Internal Gap. Once inside the Internal Gap, the moisture can be captured, guided and distilled as described in Sections C-1, C-2 and C-3.

C. Hydrodynamic and Aerodynamic Improvements

Improvements to management of waterflow on a tent's exterior and interior surfaces are made possible by the tent of this invention. Such improvements as described herein are applicable to tents with and without an Insulating Wall.

Improvements to the capture and controlled flow of condensed water within an Insulating Wall are made possible by the tent of this invention, facilitated by the introduction of an active low-pressure system that pulls air from the tent interior through a breathable Interior Membrane into the Internal Gap.

Improvements to the capture and controlled flow of rainwater within an Insulating Wall are made possible by the tent of this invention, facilitated by the introduction of an active low-pressure system that pulls air from the tent exterior through a breathable Exterior Membrane into the Internal Gap.

Improvements to the aerodynamic interactions between a tent's surfaces and forces of wind are made possible by the tent of this invention. The embodiments of aerodynamic improvements described herein are applicable to tents with and without an Insulating Wall.

C-1. Microgutter

The surfaces of a tent, including a tent's exterior surface and the interior and exterior surfaces of an Insulating Wall, may be textured with a series of dimples, bumps, ridges, ribs or other small protuberances that function as a system to collectively guide rainwater and condensation to a desired collection point or exit point. These textured surfaces, hereafter referred to as a microgutter, allow for the management of waterflow without capturing individual droplets in a channel, thus eliminating problems associated with the buildup of mildew within the walls of a confined space.

As an example of such a textured surface to control waterflow is shown in FIGS. 12A-12C. Tent 1200 has downward-sloped microgutter 1201 textured into exterior surface 1202 to move raindrops away from tent door 1203.

A magnified view of area 1204 is shown at 1210. The microgutter is a ribbing of finely grained tubular-shaped guides. These guides do not capture raindrops as would a walled, channel-type gutter. Each rib is smaller in diameter than a typical raindrop, allowing the raindrop to be guided by the slope of the rib without being captured by it.

The flow of a single raindrop on a microgutter is shown at 1220. Here, the raindrop falls on the tent surface and is pulled by gravity downward. When it comes in contact with ribbing at 1221, the raindrop is guided away from the tent door, toward the rear of the tent. The raindrop, though guided by the ribbing, is not captured and follows a path that allows it to flow over the ribbing. As this example demonstrates at 1222, the raindrop may escape the microgutter before exiting at the final dropoff location of the microgutter at 1223.

The small protuberances that guide waterflow, if existing on a tent's exterior surface, may also function as turbulence-inducing microspoilers to promote the creation of an unseparated turbulent layer. Turbulence-inducing microspoilers are further described in this document in Section C-5.

C-2. Spiral Gutter

To facilitate the management of rainwater so that it may be collected at a single exit point, a spiraling gutter may be fabricated into a tent's exterior fabric. By providing an extended pathway for rainwater through multiple revolutions around the tent perimeter, the spiraling gutter minimizes the distance from a raindrops initial point of contact to the capture point, promoting the collection of drops and therefore stimulating movement along the flow channel. The spiraling gutter also provides the advantage of a single exit location and ensures that a capture point is available to a substantial area of the tent's exterior surface.

An example spiraling gutter is shown in FIGS. 13A-13C. Tent 1300 is shown in top view at 1310, with spiraling gutter 1301 and 1311, respectively. This spiraling gutter moves rainwater to exit point 1303 and 1313 away from tent door 1302 and 1312. The path of two falling raindrops is shown at 1320. Both droplets are captured in spiraling gutter 1321 and are both ejected at exit point 1322.

C-3. Other Waterflow-Related Improvements

The surfaces of the Exterior and Interior Membranes facing into the Internal Gap may be designed with gutters or microgutters to control the flow of captured condensation.

Captured condensation may be stored for use by tent occupants or it may be directed to flow out of the tent through an evacuation chute.

As described in Section A-3, a heat source such as that of a camping stove or heat derived from solar radiation may be used to introduce a low-pressure atmosphere within the Internal Gap. This same heating system can further be used to promote the distillation of water vapor within the Internal Gap. Distilled water can be directed back into the tent as a source of potable water. Heated water can be directed back into the tent for recycled use as a heat source.

It is anticipated that tubes and other means for capturing and directing water may be incorporated within an Insulating Wall.

C-4. Aerodynamic Leading Edge

The edges of the exterior tent surface may be substantially convex in order to eliminate the introduction of turbulence normally associated with airflow striking a sharp edge. The upward-facing portion of this convex edge directs air up and across the windward surface. The downward-facing portion of this convex edge deflects air downward, outward and beneath the exterior surface towards the ground, where it has minimal impact on the controlled airflow passing over the upper portion of the convex edge. The flapping condition normally resulting from a turbulent system striking the edge is eliminated by the addition of this aerodynamic leading edge, as are the adverse impacts of turbulence acting on the air that is destined to pass over the tent.

An example aerodynamic leading edge is shown in FIGS. 14A-14C. Tent 1400 has rainfly 1401 with an aerodynamic leading edge along its entire perimeter. This leading edge is held taut by tie-downs 1403, disposed as a leading edge to winds striking the tent from a direction generally parallel to the groundplane. Edge portion 1404 is magnified at 1410 and 1420. The windward edge at 1410 shows a substantially convex surface, with undersurface 1412 of downward curvature below upper surface 1411. As shown at 1420, wind striking the edge as indicated by arrows at 1421 and 1422 is directed upward and downward by respective surfaces 1423 and 1424. The turbulent condition ordinarily associated with a sharp edged rainfly, often resulting in flapping or fluttering, is thus dampened.

C-5. Turbulence-Inducing Microspoiler

The extension of a tent's rainfly over a broad footprint streamlines the movement of high-speed winds by promoting laminar airflow, reducing the possibility that a high-pressure bubble will form on the windward side of the tent and that a low-pressure wake will follow on the leeward side of the tent.

Interactions between a high-speed layer of air moving over the tent and the tent itself may be improved by the formation of a thin layer of turbulence over its exterior surface.

Portions of the exterior surface between the perimeter edge and the mid-section of the surface may be roughened by the addition of bumps, ridges or other small protuberances, hereinafter referred to as a microspoiler. A microspoiler on the tent's exterior surface, when interacting with winds, create a thin, unseparated layer of turbulence between the tent material and a high-speed layer of laminar airflow passing over the tent. The layer of turbulence acts as a friction-reducing buffer between the tent's exterior surface and the laminar airflow, thus ensuring efficient passage of wind while minimizing adverse friction-based interactions with the tent surfaces.

An example microspoiler is shown at 1500 in FIGS. 15A-15C. Microspoiler 1501 is fabricated into exterior surface 1502 and runs around the entire perimeter of the tent. A portion of the microspoiler at 1503 is shown in an enlargement at 1510. As shown, the microspoiler is a finely-grained ribbing.

As shown at 1520, when high-speed winds 1521 meet the tent exterior at 1522, microspoiler 1523 creates a thin layer of turbulent eddies indicated in this illustration by curled arrows at 1524. This thin layer of turbulence remains between the tent's exterior surface and the outer layer of laminar airflow passing over the tent. The microspoilers are finely grained so as to ensure that the turbulent layer remains unseparated and does not promote the separation of the laminar layer away from the tent's exterior surface. This layer buffers direct interaction between the high-speed laminar layer and the tent surface.

A band of meshed netting or screen material integrated into the exterior tent surface in the area between the perimeter edge and the surface's mid-section and generally encircling the entire tent is capable of providing the dual-purpose of ventilation screen and turbulence-inducing microspoiler. A mesh allows for the entry of air underneath the exterior surface of the tent in order to provide for ventilation and evacuation of moisture. At the same time, air striking the mesh creates the unseparated boundary layer of turbulence needed to promote the efficient passage of a high-speed laminar layer of air over the tent's exterior surface.

A turbulence-inducing microspoiler can offer a secondary benefit in advantaging the tent in high winds by improving the structural integrity of a tent's outer wall, rainfly or Exterior Membrane. This benefit is particularly valuable if the material used for the exterior surface is extremely lightweight. In this configuration, a series of concentric wires are attached onto or sewn into the exterior surface, running around the tent substantially parallel to the ground-plane. The wires are slightly raised above the exterior surface so as to perturb wind moving over the exterior surface, creating a thin boundary layer of unseparated turbulence without causing separation of the laminar layer. Wires are placed with a distance that allows for the turbulence-inducing effect of a single wire to be carried to be continued by the next wire as the wind moves over the pair. These concentric wires can further be combined with a set of radial or transverse wires running through the tent's crown-point to further improve the structural integrity of the exterior surface. An example tent that employs this type of turbulence-inducing microspoiler is described and illustrated in Section D.

Microspoilers are generally anticipated to encircle the tent's exterior surface so as to advantage the tent symmetrically from winds striking the tent from any direction. On tents that are designed to be pitched with a specific orientation according to the direction of prevailing winds, a microspoiler may occupy a portion of the leading exterior surface with respect to prevailing wind.

C-6. Lift Spoilers

Winds buffeting a tent tend to run along vectors that are parallel to the ground-plane rather than along vectors that run perpendicular to the ground-plane.

To reduce the impact of forces of lift acting on tent surfaces as forces of wind pass over the tent, one or more spoilers may be integrated into the exterior surface to perturb the laminar flow of air passing over the tent. Forces of lift ordinarily impact a tent canopy as a high-speed airstream moves over the tent and separates away from the tent surface aft of the tent's crown-point.

A lift spoiler changes the point of separation of the moving airstream away from the tent surface, thus altering the center of lift. The lift spoiler is capable of reducing or eliminating the promotion of a low-pressure wake that would otherwise form in the pocket between the high-speed laminar layer of moving air above the tent and the tent's exterior surface aft of the point of separation.

Lift spoilers may be integrated into the fabric of the tent's exterior surface, or may be added onto the exterior surface. The structure of the lift spoiler may be provided by ribs, rods or spokes. Alternatively, the lift spoiler may be an airtight, inflatable bladder that is inflated when needed by the tent user.

Lift spoilers differ from the turbulence-inducing microspoilers of Section C-5 in that lift spoilers may promote the separation of a boundary layer of moving air, while the turbulence-inducing microspoilers promote the creation of an unseparated layer of turbulence between the tent exterior surface and a laminar layer of moving air.

C-7. Airstream Deflector

Winds buffeting a tent tend to run along vectors that are parallel to the ground-plane rather than along vectors that run perpendicular to the ground-plane. The airstream deflector described in this section is particularly suited to manage winds arriving along vectors parallel to the ground-plane.

An airstream deflector is capable of reducing or eliminating interactions between the high-speed airstream of gale-force winds and the occupiable portion of a tent. In use, the airstream deflector acts similarly to the windshield of a convertible automobile, creating a virtual surface over the occupied area of the vehicle over which the high-speed airstream passes.

The airstream deflector is a wedge-shaped surface that is deployed so that it comes in contact with wind in advance of the occupiable area of the tent. The airstream deflector directs wind over and to either side of the occupiable area of the tent, creating a virtual surface above and around a substantial portion of the tent's exterior surface. A laminar layer of high-speed moving air passes over this virtual surface as if it is a physical surface. The occupiable area of the tent remains protected within the low-pressure pocket that forms beneath and between the high-speed airstream passing the tent.

The airstream deflector may be a separate component of the tent. Alternatively, the airstream deflector may be integrated into the perimeter margin of the tent's exterior surface by a continuation of the same exterior surface material or by attachment to a separate type of material.

The airstream deflector works by having a slope on its windward surface that is sufficiently steep so as to cause the moving airstream to be directed above the tent and to either side of the tent. The physical surface of the airstream deflector does not have to extend over the tent because the moving layer of air that is pushed upward by the airstream deflector itself becomes a continuation of the airstream deflector's surface, acting as a virtual surface over which the high-speed outer layer of moving air passes as if it were a physical surface.

In the primary embodiment of the tent of this invention, the airstream deflector is a smooth band of upward-sloped material that is an extension of a tent's rainfly material at the rainfly's perimeter margin and separated from the rainfly by a band of air-permeable netting, screen or tether.

In another embodiment of the tent of this invention, the airstream deflector is a distinctly separate surface from the exterior surface, deployed away from the exterior surface and affixed to the ground with tent stakes.

In another embodiment of the tent of this invention, the airstream deflector has a wedge-shaped portion at its leading surface that serves to deflect arriving wind to either side of the tent.

Because the airstream deflector must redirect the forces of gale-force wind, it must have sufficient structural integrity to resist collapse. It is anticipated that the airstream deflector will require the addition of structural members such as ribs, spokes or rods. Alternatively, the airstream deflector may be deployed as an airtight bladder that is inflated to adopt and maintain a particular shape.

An example airstream deflector is shown in isolation at 1600 in FIGS. 16A-16I, with side view 1605 and top view 1610.

Camping tent 1620 includes the airstream deflector of the type shown at 1600. The occupiable area of this tent and the tent rods are all contained within the airstream deflector.

Camping tent 1630 includes airstream deflector 1631 that is attached to rainfly 1632 by a ring of meshed material 1633, unifying the tent's exterior surface. Meshing 1633 allows the tent to be adequately ventilated while rainfly 1632 protects the occupiable area of the tent from falling raindrops.

The critical function of an airstream deflector is demonstrated at 1640. Here, the path of a heavy wind buffeting the tent is shown as arrows 1641. The slope of airstream deflector at leading surface 1642 causes the deflection of the wind up and over the occupiable area of the tent. Wedge-shaped side portions of the airstream deflector, such as those portions to the side of the leading surface at 1643, cause the deflection of wind to the side of the occupiable area of the tent.

The low-pressure wake that forms aft of tent 1640 pulls the high-speed airstream downward and inward as shown by the trailing ends of arrows 1641. Although the occupiable area of the tent is protected from the high-speed airstream, it may be subject to lift and low-pressure forces acting on the rainfly so it must be suitably structured and staked to the ground to resist these forces.

The critically important feature of an airstream deflector, including the example airstream deflectors of tents shown at 1620, 1630, and 1640, is that it promotes the separate of wind away from the surface of the rainfly or occupiable area of the tent. The airstream deflector creates a virtual surface of air that is above and around the tent, over which the high-speed layer of moving air passes. Because the rainfly and other exterior surfaces of the tent do not come in contact with the high-speed airstream, these surfaces must be structured only to resist the forces of lift and of the low-pressure wake that is created beneath the virtual surface.

As shown on tent 1630, the surface of curvature of an airstream deflector is shaped with sufficient slope such that air passing off the edge of the airstream deflector opposite the perimeter edge is directed to separate away from the other exterior surfaces, here including meshing 1633 and rainfly 1632. The surface of curvature of rainfly 1632 may itself be streamlined promote laminar airflow, but it is expected to be buffered from a high-speed airstream by the virtual surface of air created by the airstream deflector.

It is possible for an airstream deflector to be completely integrated into a tent's exterior surface to form a single-piece rainfly. As shown on the example tent rainfly at 1650, the perimeter margin area of the rainfly is characterized by a surface of upward curvature that is substantially wedge-shaped or convex so as to promote the separation of wind up and away from entire central portion of the rainfly 1651 over the occupiable area of the tent. The edge at which airflow separation occurs is at inner edge 1652 of airstream deflector 1653, closest to the portion of the rainfly covering the occupiable area of the tent. The portion of the rainfly 1655 immediately following the edge of airflow separation 1652 dips downward and must, by attachment to tent rods, stakes or other structures, resist forces of lift acting on it as air separates off the airstream deflector.

Forces of low-pressure that develop as a result of the wind being redirected by an airstream deflector can be managed in a variety of ways. A series of vents integrated into of an airstream deflector can serve as intakes. A single intake vent on the leeward side of the tent may be a useful source for harnessing wind power for a small generator.

A top view of another type of airstream deflector is shown at 1660, and a side view of this airstream deflector is shown as part of a complete tent at 1670. This airstream deflector does not encircle the entire tent. Instead, the airstream deflector is deployed when winds are expected to arrive from one direction, as is the case, for example, when a tent is pitched on a shelf of a steep mountain face. Although the leeward surface of an airstream deflector may provide some aerodynamic advantage, it does not provide the substantial advantage of the windward surface and therefore may be considered optional.

C-8. Windsocks

To release pressure from beneath a rainfly or exterior tent surface, one or more windsocks may be seamed into the exterior surface to allow for the escape of rising air pressure, and otherwise collapsing onto the exterior surface in order to restrict the introduction of rainwater.

Example windsocks are shown in FIGS. 17A-17D. An inflated windsock is shown at 1700, with openings at either end of tube, tapered toward its distal end. A deflated windsock is shown at 1710, with its distal end collapsed over its proximal end to shield the tent's exterior surfaces from the entry of rainwater.

Tent 1720 has a group of windsocks 1721 seamed into exterior surface 1722, shown here in a collapsed state when air pressure under the rainfly is at equilibrium with external conditions. Tent 1730 is shown to demonstrate that under windy conditions as indicated by arrows at 1731, air enters underneath rainfly 1732 and causes a high-pressure condition. Windsocks 1733 are inflated and air escaping from the windsocks protects the rainfly from further damage.

D. Combinations

The tent of this invention may benefit from a combination of improvements described herein. The tent of this invention may also benefit from the combined effect of multiple instances of the same improvement.

For example, multiple Insulating Walls may be combined in layers. An Argon-filled Insulating Wall may be sandwiched between an outer, low-pressure airtight Insulating Wall and an inner, vacuum-pumped low-pressure air-filled Insulating Wall that functions to remove water vapor from the tent interior.

An Insulating Wall may be lined with insulative materials such as aerogels or 3M Thinsulate. The addition of a nominal layer of insulating material within the Internal Gap may be provided simply to ensure that tent will remain effective in the event of a failure of the Internal Gap to retain its internal atmosphere. If air is evacuated from the Internal Gap, a layer of insulating material can provide structural support by resisting implosive forces acting on Exterior and Interior Membranes.

The tent floor may incorporate an Insulating Wall. For construction of a tent floor with an Insulating Wall, solid layers or pressurized inflatable layers may be added to provide structural integrity. The insulating layer may itself be encapsulated inside of an air mattress, with the walls of the air mattress functioning to provide support to the Insulating Wall's Exterior and Interior membranes.

An Insulating Wall may be back-filled at low-pressure with an inert gas of lower-thermal conductivity than air. The combined effect of the low-pressure and the thermal conduction properties of the back-filled gas may be an improvement over one of the two options.

A combination tent that benefits from a variety of improvements is illustrated at side view 1880 in FIGS. 18A-18D. This tent is shown in an exploded top view at 1800, exploded bottom view at 1820 and exploded side view at 1840.

This combination tent has transparent Exterior Membrane upper portion 1801, 1821 and 1841, strengthened by the addition of concentric and transverse wires integrated into its fabric. The concentric wires are slightly raised on the tent's exterior surface to act as turbulence-inducing microspoilers. In high winds, the set of wires provide structural support to the fabric and the concentric wires create a thin layer of turbulence to act as a buffer between the tent fabric and the laminar layer of moving air.

The Exterior Membrane upper portion is flat and broad, with a gently sloped surface of curvature to improve laminar airflow across the tent surface by comparison with the relatively bluff shape of the occupiable area of the tent. The Exterior Membrane upper portion has opening 1802, 1822 and 1842 which is attached along an airtight seam to the outer opening of tent entrance 1803, 1823 and 1843. Extended portions of the Exterior Membrane upper portion fabric at 1804, 1824 and 1844 serve as feet for tent stakes, required by this tent to keep the Exterior Membrane taut.

The tent has an Exterior Membrane lower portion 1805, 1825 and 1845 which includes a substantially flat floor portion 1806, 1826 and 1846. The perimeter edge of the Exterior Membrane lower portion is attached to the perimeter edge of the Exterior Membrane upper portion by an airtight seam.

Access and Egress to the tent is provided through tube 1807, 1827 and 1847 that is attached along an airtight seam to Interior Membrane 1808, 1828 and 1848. The Interior Membrane is a bluff shape, significantly smaller in its footprint the Exterior Membrane. The Interior Membrane encapsulates the occupiable area of the tent. As shown in bottom view 1820, two insulating sleeves at 1830 enter and exit the Interior Membrane through four openings, allowing tent rods 1831 to pass through the Interior Membrane without compromising the air pressure contained within the Internal Gap. The tent rods, here shown with phantom lines, provide structural support for the entire tent.

The entire bubble of the Interior Membrane and the foot of the tent rods sit on top of the floor portion of the Exterior Membrane lower portion. Thus, the floor of the Interior Membrane is substantially coplanar with the floor of the Exterior Membrane. By encapsulating the entire Interior Membrane and tent rods within the Exterior Membrane, the tent is especially well suited to minimize interactions with wind.

Materials used for construction of the Exterior and Interior Membranes of this tent are impermeable to the passage of air. Sunlight passes through the transparent Exterior Membrane upper portion and is absorbed by the opaque Exterior Membrane lower portion and Interior Membrane. Air within the Internal Gap is heated to a temperature higher than that of the tent's external environment. Pressure relief valve 1809, 1829 and 1849 allows for escape of this heated, pressurized air within the airtight Internal Gap, until the pressure within the Internal Gap is nearly at normal atmospheric pressure. At night, in the absence of sunlight, air within the Internal Gap cools, but the relief valve restricts entry of air from the outdoors. The relatively constant volume of the Internal Gap, now contains cooled air at a pressure lower than normal atmospheric pressure, thereby providing constant thermal protection to the tent occupant.

The act of opening and closing the tent door does not compromise the pressure within the Internal Gap, specifically because the seams between the tent door tunnel and the Exterior and Interior Membranes are airtight. Because the tent door allows for the passage of outside air into the occupiable area of the tent, a zippered screen and insulated door are shown here, provided to cover the portion of the tube leading to the outside. Ventilation and removal of condensation are facilitated through this wide opening, while the majority of the tent remains protected by the Insulating Wall. 

1. A tent, the tent being characterized in that: the erected tent has a wall including an interior membrane, an exterior membrane, and an internal gap between the interior membrane and the exterior membrane, the internal gap containing a thermally insulative atmosphere. 